Microsoft's PC partners are fighting an impossible war on two fronts

Today, Microsoft, Intel, Lenovo, Dell, and HP announced a first-of-its-kind joint advertising push across TV, print, and online, with the slightly cloying slogan "PC Does What?"

The idea, Microsoft and the companies say, is to convince those many PC owners who have had their computers for the last four or five years that it's time to upgrade by showing off how far laptops and desktops have come.

If those ads convince would-be buyers to skip over Apple's Mac, so much the better.

But Microsoft's stable of PC manufacturers are setting themselves up for an impossible war on two fronts.

On one hand, they're fighting the fact that cheaper mobile devices - smartphones and tablets - are taking the place of the PC for many people, for many functions. On the other hand, they're trying to steal market share from Apple, which sells high-end computers that make up only 6 percent of the personal computing market anyway.

Only Microsoft can win this war.

Mobile on the low end

You have to feel for the PC manufacturers. Thanks to stuff like touchscreens, better batteries, and crazy-sharp screens, computers today are a lot different than the computers of a half-decade ago.

But a lot of people don't realize this. That's because in the last five years or so, consumers have been moving away from the traditional mouse-and-keyboard computing approach, and towards cheaper smartphones and tablets.

A mobile device is now the primary computer in many homes. In offices and dorm rooms, a laptop with a keyboard and mouse is par for the course. But in many households, an iPhone or Kindle Fire tablet is all people need.

So the problem isn't necessarily that Windows laptops are bad (though there is certainly room for improvement, especially on low-end models). It's that Windows itself matters less and less.

But where Microsoft's PC manufacturers are betting everything on hardware, Microsoft is future-proofing its business with subscription services that work on any device, no matter what happens to the PC market.

These PC makers don't have that luxury.

The Mac on the high end

For a long time, Apple's Mac has bucked the PC market trend by growing sales.

But Apple only accounted for 6% of the total PC market at the end of 2014, and Mac sales are slowing down for the first time in years.

Apple is fine with this niche market because it has no competition - it's the only company that makes computers running its OS X operating system, which has a distinctly different user experience than Windows. As a result, it can get away with charging relatively high prices for Macs, and plow some of the proceeds back into making new cutting-edge hardware features.

But the Windows PC market is split between Lenovo, Dell, HP, Asus, Acer, and everyone else. So even if this ad campaign steals away every single Mac customer, each vendor would probably only get a slight uplift in their sales. They're all fighting for a bigger piece of a shrinking pie.

The brutal competition between PC makers is why Microsoft made the Surface tablet and the Surface Book laptop in the first place: Its partners are so focused on cost-control to squeeze the last drops of profit from a shrinking market, Microsoft believes they don't have enough financial incentive to drive the overall PC market forward. Microsoft obviously felt the need to lead the way into the future.

If that leadership translates into a profitable hardware business for Microsoft, so much the better.

The fact that all of these business rivals teamed up for an advertising push shows that they understand the situation. But the light at the end of the tunnel may simply be an approaching train.